Home blood pressure measurements: Advantages and disadvantages compared to office and ambulatory monitoring

Abstract

Home blood pressure monitoring (HBPM) is an easy and standardized tool to measure blood pressure (BP) at home, which is recommended by several national and international guidelines to obtain reliable BP values. It is a useful and dependable measure of BP, which can add information to the more common and standardized methods, such as office (OBPM) and ambulatory blood pressure measurement (ABPM), and sometimes substitute for them. Along with ABPM, HBPM detects out-of-office BP levels, helping to identify the white-coat effect and masked hypertension. Moreover, the large number of BP measurements obtained with HBPM has been demonstrated to be associated with future cardiovascular events and to provide information on day-to-day variability; this is a new aspect, the clinical significance of which is still under evaluation. By giving patients a more active role in the management of their chronic disease, HBPM can improve treatment adherence. The present review focuses on all these aspects and describes the pros and cons of HBPM use compared to OBPM and ABPM. In conclusion, although some aspects need to be clarified, the scientific evidence collected so far should encourage the more widespread use of HBPM in clinical practice.

Key Words::

• Ambulatory blood pressure monitoring
• cardiovascular events
• home blood pressure monitoring
• masked hypertension
• white-coat hypertension

Introduction

Home blood pressure monitoring (HBPM) is a standardized tool to measure blood pressure (BP) at home, minimizing the white-coat effect and possibly reflecting future cardiovascular events better than office blood pressure measurement (OBPM). As with other kinds of BP measurement, the standardization of conditions, protocols and devices forms the basis of its meaningful use and could contribute towards the therapeutic alliance between doctors and patients.

Background

High blood pressure (BP), or hypertension, is a major risk factor for cardiovascular disease and especially stroke. The high variability of BP, with each cardiac beat having a different BP from the next, can make the measurement of the “real individual BP” challenging. Many stressors can alter BP and especially increase it, and it is well established that “office” measurement, taken by medical staff, is often biased by the “white-coat” effect. Different methods can be used to capture more reliable BP values, especially outside the medical office, where the white-coat effect should not be present. However, it is fundamental that such methods not only are more adherent to usual BP but also can reflect future cardiovascular events, as demonstrated by office BP. Along with ambulatory blood pressure monitoring (ABPM), home blood pressure monitoring (HBPM) is a feasible and reliable measure of BP, which is useful in clinical practice. The use of HBPM is recommended by several national and international guidelines for the management of hypertension, including those from the European Society of Hypertension (ESH) (1), the World Health Organization—International Society of Hypertension (2), and the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) (3).

This review summarizes the advantages and disadvantages of this type of BP measurement compared to OBPM and ABPM, with an emphasis on which aspects can be used to add value to or to substitute for the other kinds of BP measurement.

How is home blood pressure monitoring defined?

HBPM can be considered as every BP measurement that is taken by the patient or other people trained to measure the patient's BP at home, which is an environment that is familiar to the patient so that the white-coat effect can be minimized.

For diagnostic evaluation, BP should be measured daily, preferably on seven consecutive days, twice a day (in the morning and in the evening). BP should be measured in a quiet room, with the patient in the seated position, with the back and arm supported, after 5 min of rest. Two measurements should be taken on each occasion, 1–2 min apart. Other precautions that should be taken into consideration and possible pitfalls that should be avoided are discussed in more detail in other reviews of BP measurement (4,5), and are summarized in Table I, focusing on HBPM.

Table I. Aspects that require attention when measuring blood pressure, and especially home blood pressure.

Preliminary procedures	Measurement procedures
Patient training (short for automated devices)	Quiet and temperate environment
Use of validated devices, preferably an oscillometric automatic device	Avoid physical activity (at least 5 min rest), smoking, coffee and alcohol intake before measurement
Periodically check for accuracy	Avoid talking, reading, watching television and eating during measurement
Adequate cuff and bladder size (covering 80–100% of the arm circumference)	Sitting position suggested, with back and arm supported
Upper arm cuff suggested (use wrist cuff only if brachial BP measurement is impossible, e.g. in severe obesity)	Upper arm at the level of the heart
	Immediate reporting of all readings

BP can be measured either manually by another person trained to measure BP using an anaeroid device or semiautomatically using a validated device. International guidelines suggest the use of oscillometric monitors; auscultatory devices, such as anaeroid or mercury, are generally not recommended, except under specific conditions, such as arrhythmia, where oscillometric devices could be inaccurate (6). Because a multitude of devices is available on the market, physicians and patients should be certain that the monitor they purchase has been validated according to international validation protocols. A couple of websites where the validation of devices is presented are: www.dableducational.org and www.bhsoc.org.

Once a patient has been introduced to HBPM, it is important that the physician verifies both the patient's technique and the accuracy of the device. Physicians should give patients clear instructions about the choice of the device and its correct use, and about the interpretation of home BP readings, to reduce the likelihood of errors during measurements and to make patients more familiar with their disease and its management. The use of CD-ROMs and booklets or access to websites can be useful.

Moreover, the accuracy of the monitor should be checked periodically. An easy and rapid protocol has been proposed: five sequential same-arm BP readings are taken, about 30 s apart; the first two readings are taken by the patient with their device, the third by the physician using a mercury sphygmomanometer, the fourth by the patient and the fifth by the physician (7). A comparison of the readings can assess the accuracy of the device. Although there are no established criteria for determining acceptability, a difference of 5 mmHg could be a reliable cut-off. Unlike anaeroid and mercury devices, for which periodical validation is needed, oscillometric devices are unlikely to develop calibration errors. However, occasional checks are useful for these monitors.

During the measurement, the patient should be advised to avoid all the factors that can influence BP levels, such as the recent intake of coffee or alcohol, smoking, physical activity, emotions and an uncomfortable environment. The patient should be seated and with the back supported, and should place the cuff in the correct position on the upper arm and keep the arm resting on a table at the level of the heart.

It is preferable that the results are directly stored in a memory-equipped device or reported in a standardized logbook immediately after each measurement (6).

Why is home blood pressure monitoring so useful?

It has been demonstrated that self-measurement of BP at home is a good tool to estimate “real” BP levels outside the office; in particular, HBPM compares well with intra-arterial BP measurement in healthy young men (8). HBPM is also comparable to OBPM in treated hypertensive subjects, when measured with the same semiautomatic device (9).

HBPM can therefore help in the identification of patients with white-coat hypertension (WCH) and those with masked hypertension. WCH is a common condition in patients and is defined as the presence of home BP control despite elevated office BP. Well-trained patients can perform home BP measurements with precision and the comparison with office BP levels can suggest the presence of some degree of white-coat effect (10). It is important to detect WCH in order to identify normotensive patients with white-coat effect and, in hypertensive patients, to confirm or reject the diagnosis of resistant hypertension. The underestimation of WCH can lead to overtreatment in a category of patients with a cardiovascular risk as low as in normotensives, as indicated by several prognostic studies (11,12). However, other studies comparing office and out-of-office BP monitoring with a longer follow-up report a risk of cardiovascular events similar to that of patients with sustained hypertension (13–15).

Masked hypertension also occurs frequently and is often underdiagnosed. Patients with masked hypertension have controlled office BP and elevated out-of-office BP. These subjects need a closer assessment of their BP levels and a consequent adjustment of therapy, because their cardiovascular risk is similar to that of sustained uncontrolled hypertensive patients (14,16).

Current guidelines recommend the use of ABPM to detect the above-mentioned conditions. Besides this method, HBPM can also be useful and is therefore suggested by the ESH (6).

Moreover, HBPM is inexpensive. A recent study showed that HBPM used alone in the management of hypertension presents lower costs than OBPM and ABPM, without significant differences in BP control (17).

The indications for HBPM are listed in Table II.

Table II. Indications for home blood pressure monitoring.

All patients receiving antihypertensive drugs, especially those who need closer control (e.g. resistant hypertension, hypertension in pregnancy)

To evaluate resistant hypertension

To evaluate white-coat effect and white-coat hypertension

To evaluate masked hypertension

To improve treatment compliance and persistence

Predicitivity of future cardiovascular events

HBPM seems to be a reliable predictor of cardiovascular mortality and morbidity, and therefore the available evidence and recent guidelines suggest the use of HBPM for prognostic assessment (6,18).

When the prognostic significance of OBPM was compared to out-of office (24 hand home) BP measurement, out-of-office BP monitoring was found to be superior to OBPM for the prediction of major cardiovascular events (cardiovascular death, myocardial infarction and stroke) in older patients in general practice, and the prognostic value of BP measured at home was at least equal to that of daytime ambulatory BP. Moreover, patients with WCH had an outcome similar to that of normotensive subjects (19).

The results from the Finn-Home study suggest a superiority of HBPM over OBPM in predicting cardiovascular events, and systolic HBPM was the sole predictor of total mortality (20).

Data from a review of eight large long-term prospective studies, concerning the comparison of the prognostic ability of home versus OBPM, suggest that the cardiovascular risk is better predicted by HBPM than by office measurement, independent of the number of readings (18). From this preliminary analysis, it seems that patients with the white-coat phenomenon have a low cardiovascular risk, similar to those with controlled office and home BP, whereas subjects with masked hypertension are at increased risk, like uncontrolled hypertensives (18).

In a meta-analysis including 5008 individuals without antihypertensive treatment from five populations, hazard ratios associated with 10 mmHg increases in systolic home BP were computed across conventional BP categories, identified on the basis of European and American hypertension guidelines. The results show that home BP substantially refines risk stratification at conventional BP levels assumed to carry no or mildly increased risk, in particular at high to normal conventional BP, and in mild hypertension the hazard ratios were 1.24 and 1.20, respectively, for all cardiovascular events (21).

Consequently, HBPM could be used as an additional tool to classify patients into different risk categories.

Blood pressure variability

Recent studies have shown that the variability in BP levels between different visits has an important prognostic significance (22,23). HBPM can provide information about day-to-day BP variability, which appears to have an important and independent role in the onset and worsening of target organ damage. Although there is no consensus on the optimal variability index of HBPM, and at present it remains of limited value in clinical practice, several studies and a recent systematic review have addressed its prognostic value for preclinical cardiac, vascular and renal damage (24–26). There is no clear evidence about the prognostic ability of home BP variability for major outcomes, such as cardiovascular events and total mortality. The Ohasama study compared the predictive power of mean home BP levels with day-by-day home BP variability for cognitive decline, and found that the day-by-day variability in systolic home BP was significantly associated with cognitive decline beyond average systolic home BP (27). On the other hand, in a recent study the comparison of variability indices derived from ABPM and HBPM showed no association with target organ damage (left ventricular mass index, urinary albumin-to-creatinine ratio and pulse-wave velocity) by either measurement method, except for 24 h monitoring and pulse-wave velocity (28). In another study, the day-by-day variability in home BP, especially systolic BP, was associated with carotid artery atherosclerosis and endothelial function in normotensive and mildly to moderately hypertensive subjects, with the variability in home BP increasing with increasing BP level (29).

Home blood pressure monitoring and treatment adherence

As well as providing important information on the individual responsiveness to antihypertensive treatment, HBPM may serve as an intervention to improve BP control and patients’ adherence to treatment. Low adherence is common, especially with regard to lifestyle changes, but rapidly extends to drug prescription; after 6 months more than one-third and after 1 year about half of the patients may stop the prescribed therapy (30). Several approaches have been proposed, including improvement not only of patients’ but also of doctors’ involvement in their approach to chronic disease, and strategies to overcome the deficiencies of healthcare systems (Table III). Self-monitoring should be included in an educational intervention on patients, to encourage them to be actively involved in their chronic disease and its management.

Table III. Adherence-enhancing strategies.

Patient	Information and motivational strategies
	Self-monitoring of blood pressure
	Group sessions
Drug treatment	Simplification of drug regimen
	Reminders
Health system	Intensified care, including telemonitoring of home blood pressure
	Involvement of pharmacists

Self-monitoring of BP can contribute to better BP control through different mechanisms: improving treatment adherence, medication persistence and lifestyle changes. The evidence on the effects of BP self-monitoring on treatment adherence is encouraging; however, evidence of its effects on the other factors is still scarce and apparently of little clinical relevance (31).

In the past few years, attention has been paid to treatment adherence in resistant hypertensive patients and efforts have been made to identify easy and useful tools to detect adherence.

Recent studies in patients who were classified as resistant checked the adherence to treatment by measuring serum drug concentrations. The results showed that about half of hypertensive patients were not adhering to their treatment, at least to one prescribed drug, and 9–34% of them did not take any antihypertensive medication (32–34). Along with the available tools, such as “directly observed therapy clinics”, questionnaires or BP telemonitors, the results of these studies suggest that assessment of serum drug levels may be a helpful and relatively easy way to detect non-adherent patients in order to avoid overprescription and to prevent an extensive evaluation of the possible causes of resistant hypertension.

Some clinical trials in the past few decades have tested the effect of HBPM on medication adherence in clinical and non-clinical settings, and many of them showed an increase in therapy compliance, especially in trials where HBPM was tested together with other adherence-enhancing strategies. In particular, the association of HBPM with objective electronic monitoring showed good results (35–38), but pill counts together with HBPM are a useful compliance-enhancing strategy (39). Other studies, which used self-reports or pharmacy refills, did not show positive findings (35,40).

The studies comparing HBPM to OBPM show that patients using HBPM achieve better BP control than those undergoing usual BP measurements. A meta-analysis of 18 randomized controlled trials found that hypertensive patients achieve better BP control with HBPM than with standard BP monitoring (standardized mean difference: systolic BP 4.2 mmHg, diastolic BP 2.4 mmHg) and the relative risk of BP above target was lower in patients using HBPM (risk ratio 0.9) (41).

A recent clinical trial showed that, among high cardiovascular risk patients with hypertension, self-monitoring of BP with self-titration of antihypertensives resulted in a lower systolic BP at 12 months compared with subjects receiving usual care (42).

Interpretation of home blood pressure monitoring and definition of hypertension

Since HBPM can be highly variable, single-occasion measurements can be misleading. Therefore, the clinical decision should be based on the average of many BP readings, taken on different days. An important reduction or elevation in BP levels should be taken into account if it is persistent or associated with symptoms, even if isolated.

National and international guidelines suggest similar levels for the definition of hypertension. Table IV reports the diagnostic criteria proposed in the 2013 guidelines for the management of arterial hypertension by the ESH/European Society of Cardiology (30).

Table IV. Criteria for the definition of hypertension by office (OBPM), ambulatory (ABPM) and home blood pressure monitoring (HBPM).

Category	Systolic		Diastolic
OBPM
Optimal	< 120	and	< 80
Normal	120–129	and/or	80–84
High normal	130–139	and/or	85–89
Grade 1 hypertension	140–159	and/or	90–99
Grade 2 hypertension	160–179	and/or	100–109
Grade 3 hypertension	≥ 180	and	≥ 110
Isolated systolic hypertension	≥ 140	and	< 90
ABPM
Hypertension: day-time or awake	≥ 135	and/or	≥ 85
Hypertension: night-time or asleep	≥ 120	and/or	≥ 70
Hypertension: 24 -h	≥ 130	and/or	≥ 85
HBPM
Hypertension	≥ 135	and/or	≥ 85

A recent meta-analysis compared HBPM and conventional BP measurements in order to identify different BP thresholds for gender and age; the results support current guidelines that indicate a single threshold across ages and in both genders (43).

Home blood pressure monitoring in special populations

The use of HBPM should be carefully considered in some special conditions.

In adults, some features and some clinical conditions, such as obesity, the presence of arrhythmias, chronic kidney failure and diabetes mellitus, may reduce the accuracy of oscillometric devices.

In obese people, attention should be paid to adequate cuff size, depending not only on arm circumference but also on arm shape. In some cases these difficulties can be avoided by the use of a wrist device, but further investigation and validation of devices are needed. Moreover, in obese patients the prevalence of both WCH and masked hypertension seems to be higher, making HBPM a useful tool to determine the real BP levels in these patients (6).

The presence of arrhythmias makes accurate BP measurement difficult or impossible, in particular in the case of atrial fibrillation without rate control, because of the large variation in BP from beat to beat. In patients with arrhythmias, after appropriate training, the auscultatory method remains more reliable, at least until devices with special arrhythmia-detection algorithms have been validated (6).

Patients with chronic renal failure and diabetes represent two special populations in which closer BP control is needed. In these patients, HBPM is a recommended tool to obtain more reliable BP levels, and this BP monitoring method has a better prognostic value compared to OBP. However, these patients are more likely to have higher arterial stiffness, which is typical of these conditions, so reducing the accuracy of oscillometric devices, and not all monitors have been validated in these populations (6).

The use of HBPM could also be explored in two other populations: children and pregnant women.

During the past few decades, increasing attention has been paid to BP in children. HBPM appears to have considerable importance in clinical practice in children and adolescents, and therefore its use was suggested by the ESH in the Second International Consensus Conference on Home Blood Pressure Monitoring (6).

A recent systematic review and meta-analysis suggested a moderate but significant association between out-of-office BP and preclinical organ damage in children and adolescents, but the evidence comes from studies based on ABPM, whereas the role of HBPM remains controversial because of limited published evidence (44).

Moreover, uncertainty remains on reference values, and evidence on the accuracy of oscillometric devices in this population is very limited (see www.dableducational.org).

The accuracy of oscillometric devices could be reduced in pregnancy, especially pregnancies complicated by pre-eclampsia, in which the altered haemodynamics often results in the underestimation of BP. In these cases, only a few monitors have been validated by acceptable studies. Although no established thresholds are available, HBPM could help in BP assessment during pregnancy, in order to detect altered BP levels earlier and to facilitate closer monitoring, with a reduction in the number of visits and the related anxiety (6).

The advantages and disadvantages of HBPM compared to both OBPM and ABPM are presented in Table V. This can serve as a practical guide for clinicians dealing with people with high BP.

Table V. Advantages and disadvantages of using home blood pressure monitoring (HBPM) compared to office blood pressure (OBPM) and ambulatory blood pressure monitoring (ABPM).

Advantages and disadvantages of HBPM vs ABPM
HBPM	ABPM
More time to adequately instruct the patient	Less time to instruct the patient
More controlled by the patient	More controlled by the doctor
Once purchased, can be repeated indefinitely without added costs	Relatively expensive
Possible reporting bias	Possible technical errors
Probably more useful to evaluate the effect of therapy measuring BP over a longer period	Gives information about the effect of BP medication only on the day of ABPM
Can give information about day-to-day variability (the clinical significance of which is still under evaluation)	Can give information about short-term BP variability, including nocturnal dipping (for which there is more evidence of clinical significance)
Can give more information about specific situations, e.g. drug-induced hypotension or post-prandial hypotension	Can give more information about specific situations, if present on the day of registration
Gives information only when patient is awake at home	Gives information about BP during daily activity and during sleep, including possible clues about secondary forms of hypertension, e.g. obstructive sleep apnoea
Detection of white-coat effect and masked hypertension, but few studies on prognostic significance	Detection of white-coat effect and masked hypertension, and more studies on prognostic significance
Detection of true resistant hypertension	Detection of true resistant hypertension
Can favour adherence to treatment by giving the patient a more active role	Probably not useful to enhance adherence
Advantages and disadvantages of HBPM vs OBPM
HBPM	OBPM
Minimizes white-coat hypertension and white-coat effects	Prone to white-coat hypertension and white-coat effects
Potentially more practical to evaluate the effect of therapy, measuring BP more often and over a longer period	Less practical to evaluate the effect of therapy
More controlled by the patient	More controlled by the doctor
Gives information about day-to-day BP variability (the clinical significance of which is still under evaluation)	Gives information about visit-to-visit BP variability (for which there is more evidence of clinical significance)
Can give information about specific situations, e.g. drug-induced hypotension or post-prandial hypotension	More studies on prognostic significance
Detection of true resistant hypertension	Less useful to detect true resistant hypertension
Less standardized diagnostic criteria	Standardized diagnostic criteria
Can favour adherence to treatment by giving the patient a more active role	Reduced risk of self-medication
Gives information about BP at home and after home activities	More difficult to implement in underdeveloped countries

BP, blood pressure.

Gaps in the evidence

Some issues are still a matter of debate and would benefit from further investigation:

• What are the optimal home BP target levels?

• Do patients benefit from out-of-office BP control over standard (office) BP control?

• What is the prognostic significance and clinical relevance of HBPM?

• What impact does HBPM have on treatment adherence?

Conclusions

Strong evidence is available to encourage the use of HBPM in clinical practice, although many points need to be better understood and elucidated. Self-monitoring of BP at home is easy and inexpensive, and it can provide a large number of measurements which are likely to be more reliable than those obtained by OBPM and to be associated with future cardiovascular events. However, two preliminary items are essential when HBPM is proposed to the patient: first, the physician should become familiar with this technique, its applications and its limits; and, secondly, the patient should receive the correct instructions and training. In conclusion, HBPM is a reliable technique to obtain important information about patients’ BP in the home environment. The time spent on carefully informing and training the patient in this technique is counterbalanced by the potential increase in the prediction of cardiovascular events and in patients’ adherence to antihypertensive therapy. Other measures obtained by HBPM, such as day-to-day variability and its use in special populations, along with its effects on treatment adherence and optimal home BP target levels, require further in-depth research.

Declaration of interest: The authors report no conflicts of interest. The study received no financial support.